Nicotine, as consumed through tobacco use, is a drug abused by nearly 47 million Americans. Understanding the consequences of nicotine exposure is therefore a major health issue in the United States and of interest at epidemiological, clinical and basic science levels. Of particular concern are the approximately 20% of women who smoke, two-thirds of whom continue to do so during pregnancy. Epidemiological studies link maternal smoking to low infant birthweight, reduced head size, congenital heart defects, isolated craniosynostosis, craniofacial anomalies, and limb malformations. As nicotine is a major toxic component of tobacco smoke and is present at equivalent levels in fetal and maternal tissues, it is strongly implicated as a causative agent of such defects. The physiological effects of nicotine are exerted by activation of nicotinic acetylcholine receptors (AChRs). AChRs are pentameric, ligand-gated ion channels, ubiquitously expressed in both the central and peripheral nervous systems, as well as in skeletal muscle. Thus, in addition to the established functions of AChRs in signaling, addiction, task attention, and neurological disease, AChRs are also likely to participate in smoking-related birth defects. The ability of nicotine to cause such defects is consistent with the appearance of AChRs in neuronal precursors and in the human CNS prior to cortical development. The early appearance of AChRs and their known ability to influence neuronal survival and process outgrowth directly implicate them in normal neuronal development in vivo. At present, however, developmental roles for AChRs are novel and remain poorly understood. This proposal will analyze the developmental significance of neuronal AChRs using the embryonic chick ciliary ganglion (CG) as a model system. CG neurons are ideally suited for such studies because they express well-defined AChR types having distinct properties and unique functions. Moreover, the CG is accessible to manipulation throughout development, both in vivo and in cell culture. A major AChR type is sensitive to blockade by (-bungarotoxin ((Bgt). The investigator has previously shown that these (Bgt-AChRs influence process outgrowth and promote neuronal survival in culture. Further, preliminary studies suggest that (Bgt-AChRs can influence synapse formation on CG neurons in culture. The experiments described here will extend these findings to the in vivo setting using retroviral delivery of mutated AChR genes into embryos during neuronal development. These alterations will be assessed for their impact on neuronal survival (Aim 1), synapse formation (Aim 2), and AChR distribution (Aim 3). The proposed studies are expected to provide new information concerning the developmental significance of AChRs in vivo. Fulfilling the goals of this project will aid in developing the investigator's scientific independence and is expected to reveal additional clues for understanding how nicotine abuse contributes to birth defects.